Up until now, there has been proposed an automotive vehicle which comprises a drive source such as an internal combustion engine, an electric motor and the like, and vehicle wheels drivably connected with the drive source through a power transmission train to enable the driving force from the drive source to be transmitted to the vehicle wheels through the power transmission train. The power transmission train with which the drive source is drivably connected is apt to generate a muffled sound and a “jara sound” originated for example from the rotation fluctuation caused by the torque fluctuation of the internal combustion engine.
The term “jara sound” is intended to indicate an abnormal sound generated by the idling gear sets of the transmission gear sets collided by torsional vibrations originated from the rotation fluctuation caused by the torque fluctuation of the internal combustion engine. The term “muffled sound” is intended to indicate an abnormal sound generated in the passenger room by the vibrations caused by the torsional resonance of the power transmission train having the torque fluctuation of the internal combustion engine as a vibratory force. The torsion resonance of the power transmission train exists in the normal drive area (for example about 2500 rpm of the rotation number of the internal combustion engine for the “FF” vehicle) of the internal combustion engine of a vehicle travelling at a low speed.
In view of this problem, usually provided is a torsional shock absorbing apparatus, i.e., a damper mechanism between the internal combustion engine and the power transmission train to absorb the rotation fluctuation of the internal combustion engine, and thus to absorb the torsional vibrations of the power transmission train.
There has so far been known a torsional vibration absorbing apparatus which comprises a first rotation member selectively engaged with or disengaged from a flywheel, a second rotation member drivably connected with an input shaft extending from a transmission, and a coil spring having the first rotation member resiliently connected with the second rotation member in the rotation direction of the first and second rotation members (for example see Patent Document 1).
The first rotation member is constituted by a clutch disc, and a pair of side plates secured to the inner peripheral portion of the clutch disc. The second rotation member is constituted by a hub which in turn comprises a boss splined to the outer peripheral portion of the shaft, and a flange portion formed to extend radially outwardly of the boss.
The coil spring is supported on a plurality of spring accommodating windows formed in the flange portion, and a pair of spring accommodating portions formed on the pair of side plates in the face-to-face relationship with the spring accommodating windows, respectively.
The coil spring thus constructed is compressed in the circumferential direction of the input plate between the pair of input plates and the hub, when the pair of side plates and the hub are relatively rotated with each other. The coil spring thus compressed can absorb the circumferential direction torsional vibrations inputted to the hub by the pair of side plates and suppress the “jara sound”.
On the other hand, there is provided a hysteresis mechanism constituted by a thrust member disposed between the hub and the pair of the side plates to generate hysteresis torque caused by the frictional force between the hub and the pair of the side plates, and thus to suppress the torsional resonance of the power transmission train, thereby making it possible to lessen the muffled sounds remarkably increased in the vehicle room at the slow speed travelling of the vehicle.
On the other hand, it is well known that the internal combustion engine has fluctuation properties different at the acceleration time of the vehicle when the rotation torque is transmitted from the pair of the side plates to the hub to have the hub rotated with the pair of the side plates at a positive rotation side, from at the deceleration time of the vehicle when the rotation torque is transmitted from the hub to the pair of the side plates to have the hub rotated with the side plates in a negative rotation side.
FIG. 9 is a graph showing the relationship of the rotation fluctuations of the internal combustion engine at the acceleration time and at the deceleration time of the vehicle. As shown in FIG. 9, the rotation fluctuation of the internal combustion engine at the acceleration time is large in the low rotation speed area of the internal combustion engine, while the rotation fluctuation of the internal combustion engine at the deceleration time is large in the high rotation speed area of the internal combustion engine
For this reason, it is required that the hysteresis torque of the damper mechanism increased at around the resonance point at the acceleration time of the vehicle causes the torsional resonance of the power transmission train in the low speed rotation area of the internal combustion engine to be suppressed, while the hysteresis torque of the damper mechanism decreased in the high speed rotation area with the large fluctuation of the internal combustion engine at the deceleration time of the vehicle causes the attenuation force to be increased to suppress the torsional vibrations.
The conventional damping apparatus is, however, set to have a single hysteresis at the acceleration and deceleration times, thereby resulting in the fact that the hysteresis set to be large in the damping apparatus can attenuate the torsional vibrations of the power transmission train in the low speed rotation area of the internal combustion engine at the acceleration time of the vehicle, however, is apt to make it impossible to sufficiently attenuate the torsional vibrations at the deceleration time of the vehicle.
In the case that the hysteresis torque is decreased for the purpose of absorbing the torsional vibrations at the deceleration time of the vehicle, the torsional resonance of the power transmission resonance causes the torsional vibrations to be increased at around the resonance point at the deceleration time of the vehicle, thereby leading to generating the muffled sounds (see dotted line in FIG. 10).
In contrast, another torsional shock absorbing apparatus of this kind is proposed to change the hysteresis torque at the acceleration time and at the deceleration time. The above torsional shock absorbing apparatus comprises a friction generating mechanism intervening between the pair of side plates and the hub to generate frictional force when the pair of side plates and the hub are relatively rotated with each other. The friction generating mechanism is constituted by a first friction generating portion for generating the frictional force between the pair of side plates and the hub in the positive and negative rotation sides of the torsional property, and a second friction generating portion for not generating the frictional force between the pair of the side plates and the hub, resulting from the fact that the side plates are not engaged with the hub in the negative rotation side of the torsional property (for example see Patent Document 2).
The above torsional resonance apparatus can suppress the torsional resonance by increasing the hysteresis torque at the acceleration time of the vehicle, and thus can increase the attenuation force by decreasing the hysteresis torque at the deceleration time of the vehicle.